Induction of Anesthesia with Small Doses of Sufentanil or Fentanyl

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Abstract
The purpose of this study was to examine the dose versus EEG response relationship, the speed of onset, and the thiopental requirement for induction of anesthesia with small doses of sufentanil and fentanyl. The power spectrum of the electroencephalogram (EEG) was used to quantify the effect of the opioids. Eighty male surgical patients, 52–80 yr old, were randomly divided into eight groups of ten to receive fentanyl, 5, 7, 10, or 13 μg/kg, or sufentanil, 0.5, 0.7, 1.0, or 1.3 μg/kg. The opioid was given iv over 1 min at a constant rate of infusion. Three to four minutes after the start of the opioid dose, thiopental was given iv in 25 mg increments every 30 s until the patient was unconscious. Power in the 1–3 Hz band reached maximum levels in less than 4 min after the start of opioid administration. At fentanyl doses of 7.0 μg/kg or less, or sufentanil doses of 1.0 μg/kg or less, the EEG effects did not increase in proportion to the dose of opioid. There was not a significant difference in the maximum power achieved in the 1–3 Hz band for sufentanil, 0.5, 0.7 and 1.0, and fentanyl, 5 and 7 μg/kg. Doses of fentanyl, 10 or 13 μg/kg, or sufentanil, 1.3 μg/kg were substantially more effective; the maximum power increased significantly between 7 and 10 μg/kg of fentanyl and 1.0 and 1.3 μg/kg of sufentanil (P < 0.0001). The potency of sufentanil and fentanyl were compared by superimposing, the dose versus response (power) curves. The potency ratio was 1:8 (sufentanil:fentanyl). Speed of onset (T50) was determined from the time required to reach 50% of the maximum power in the 1–3 Hz band. Mean T50 was similar for sufentanil, 0.5, 0.7, and 1.0 μg/kg (132 ± 21 s, including the 60 s drug injection) and fentanyl, 5 and 7 μg/kg (132 ± 20 s). Mean T50 was significantly less (P < 0.0001) for sufentanil, 1.3 μg/kg (92 ± 22 s) compared with that following an equipotent dose of fentanyl, 10 μg/kg (112 ± 18 s). The thiopental dose requirement was inversely related to the dose of opioid and was less for sufentanil compared with fentanyl. Nine of ten patients receiving 1.3 μg/kg sufentanil did not require thiopental to produce unconsciousness.